Many uses have been proposed for nanoparticles including armor, surface coating, data storage, inks, bio-imaging applications, and sinter resistant catalysts. The recent demonstration of complex nanoparticles, that is nanoparticles with multiple shells, and/or designed void spaces, suggests other applications such as anode or cathode materials for high energy density batteries, and light, high energy density solid fuels. Enabling these technologies will require means to make large quantities of nanoparticles.
There are many processes for making primarily metallic nanoparticles including several aerosol techniques such as aerosol-through-plasma (A-T-P) including evaporation of solvents from small drops containing dissolved salts and flame synthesis. Non-aerosol processes for making nano-sized metal particles include metal gas evaporation, metal evaporation in a flowing gas stream, mechanical attrition, sputtering, electron beam evaporation, electron beam induced atomization of binary metal azides, expansion of metal vapor in a supersonic free jet, inverse micelle techniques, laser ablation, laser-induced breakdown of organometallic compounds, and pyrolysis of organometallic compounds between others. It is, however, still desirable to provide methods for generating metal particles using a simple and rapid process.
Additionally, particles sized in the micron to sub-micron range are needed to enable a host of existing technologies. Currently, there are no practical methods for economically making micron and sub-micron sized metal particles.
For example, particle injection molding (PIM) process is less expensive than other conventional process (e.g., machining) and currently employed to create metal parts of ca. 100 microns or less. PIM is a process involving creating objects by injecting metal/wax composites into molds, followed by removing the wax. Parts of nearly every electronic device are made using PIM processes including computers, cell phones, cameras, and watches. The average automobile produced today has nearly 50 lbs of injection molded parts. Also, high tech mini-drills, some dental implants, etc. use parts made by PIM.
A critical rule of PIM generated parts is that the particles used should have a size about 5% of the minimum part dimension. At present, there is no efficient process for creating metal particles with a median size, e.g., of less than about 5 microns. The standard commercial methods including high pressure atomization or water atomization have reached asymptotic limit and do not result in smaller size. This absence of a suitable technology means that PIM is economic only for objects greater than 10 microns in dimension. Even with more energy, higher pressure, etc, metal particles are not generated in the micron/sub-micron size.
It is also notable that there are applications for carbon and graphite coated metal particles. For example, graphite coated particles may be used in next-generation lithium compound batteries. In another example, carbon or graphite coating may eliminate or reduce sinter rate of metal particles employed in high temperature (ca. >250° C.) applications, such as high temperature catalysis.
Hence, it is desirable to provide a method or process capable of producing metal particles and alloys in the micron or sub-micron size range. It is also desirable to provide a method or process capable of producing metal particles and alloys that are carbon or graphite coated in the nano, sub-micron, or micron size range. It is further desirable to provide a simple and rapid process.